Donald Trump faced an embarrassing plagiarism scandal Tuesday that tarnished his wife Melania's prime-time speech to a Republican National Convention already roiled by an opening day rank-and-file revolt.

It was a rough start to the four-day buildup to Trump's presidential nomination, one designed for maximum media exposure for the Republican standard bearer and his supporters.

With millions watching on TV at home, Melania Trump delivered a defense of her husband and his bid to be the next president of the United States before thousands of cheering convention delegates.

But unmistakeable similarities between a passage in her speech about her guiding values and one in a speech given by Michelle Obama at the 2008 Democratic convention soon came to light.

A senior Trump communications adviser, Jason Miller, acknowledged in a statement that Melania Trump's team of writers "in some instances included fragments that reflected her own thinking."

The development came after a chaotic start to the Republican gathering in Cleveland, which erupted in jeers from Trump opponents after they were denied a chance to speak.

"We deserve to be heard, this is the people's convention!" said Diana Shores, a delegate from Virginia, while pro-Trump delegates tried to drown out the rebels with shouts of "Shame! Shame!"

Many are furious that the party of Abraham Lincoln and Theodore Roosevelt will be led by a man who described Mexicans as rapists and advocated barring Muslims from entering the country.

But Trump fans insisted delegates heed the will of the grassroots of the party and make him the Republican nominee without equivocation.

The billionaire won a thumping victory in a series of statewide party elections, garnering more than 13 million votes -- the most of any Republican nominee ever.

This was meant to be Trump's moment -- the point at which he put the lid on Republican divisions and marched the party toward November's election and the White House.

Making a surprise cameo appearance at the gathering in Cleveland to introduce his wife, the bombastic tycoon showed confidence that belied the day's spasm of public division.

"We're going to win so big" said Trump. "Ladies and gentlemen, it is my great honor to present the next First Lady of the United States."

Ahead of the convention he had tried to assuage conservative critics and bring the party together by naming Indiana Governor Mike Pence as his running mate.

But it was Trump's Slovenian-born wife Melania, until now only a minor presence in the campaign, who stepped up as his chief advocate on the convention's opening day.

She took the stage with all the allure of a former model and in a strong accent made the case for Americans to entrust Trump with the presidency.

"Donald is, and always has been, an amazing leader," said the 46-year-old. "Now, he will go to work for you."

"He does not give up," she said of her husband, portraying him as a loving father and successful businessman who would be a strong and compassionate president.

"If you want someone to fight for you and your country, I can assure you, he's the guy," she said.

She also sought to put a more human face on a candidate many voters see as brash and egotistical.

"Donald intends to represent all the people, not just some of the people. That includes Christians and Jews and Muslims. It includes Hispanics and African-Americans and Asians and the poor and the middle class."

No sooner had the speech been delivered, though, than it was overshadowed by the plagiarism controversy.

In a passage that appeared to be lifted from Michelle Obama's speech eight years ago, Melania discussed her parents influence.

"My parents impressed on me the values: that you work hard for what you want in life. That your word is your bond and you do what you say and keep your promise. That you treat people with respect. They taught me to show the values and morals in my daily life. That is the lesson that I continue to pass along to our son," Melania Trump said.

"And we need to pass those lessons on to the many generations to follow. Because we want our children in this nation to know that the only limit to your achievements is the strength of your dreams and your willingness to work for them."

In her 2008 speech, Michelle Obama said:

"And Barack and I were raised with so many of the same values: that you work hard for what you want in life; that your word is your bond and you do what you say you're going to do; that you treat people with dignity and respect, even if you don't know them, and even if you don't agree with them.

"And Barack and I set out to build lives guided by these values, and pass them on to the next generation. Because we want our children -- and all children in this nation -- to know that the only limit to the height of your achievements is the reach of your dreams and your willingness to work for them."